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Evidence for Neptunium Incorporation into Uranium (VI) Phases

Published online by Cambridge University Press:  17 March 2011

Edgar C. Buck ,
Brady D. Hanson ,
Judah I. Friese ,
Matt Douglas  and
Bruce K. McNamara
Edgar C. Buck
Affiliation:
Environmental Technology Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA 99352, edgar.buck@pnl.gov
Brady D. Hanson
Affiliation:
Environmental Technology Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA 99352
Judah I. Friese
Affiliation:
Environmental Technology Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA 99352
Matt Douglas
Affiliation:
Environmental Technology Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA 99352
Bruce K. McNamara
Affiliation:
Environmental Technology Division, Pacific Northwest National Laboratory, 902 Battelle Blvd., Richland, WA 99352
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Abstract

This paper examines the ability of electron energy-loss spectroscopy (EELS) combined with transmission electron microscopy (TEM) to detect both low concentrations of Np in a U matrix and to provide evidence for incorporation of Np in U(VI) phases. The case for U(VI) secondary minerals acting as solubility-controlling phases for Np in repository performance assessment models has not been fully established. Direct evidence for incorporation, rather than sorption, continues to be difficult to obtain. Detection of Np with TEM-EELS is hampered by the occurrence of a plural (multiple) scattering event from the more abundant U atoms (U-M5 + U- O4,5), that results in severe overlap on the Np-M5 edge at ∼3665 eV. By examining the energy âgap' between the Np-M5 and Np-M4 edges (184 eV), a method for observing Np independently of the plural scattering event has been established. Clear evidence of Np incorporation into synthetic studtite {(UO2)(O2)(H2O)2](H2O)2} and uranophane {Ca(UO2)2(SiO3OH)2(H2O)5} has been found with TEM-EELS. The EELS technique continues to remain an important tool for examining the potential for transuranic behavior in nuclear waste materials.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 824: Symposium CC – Scientific Basis for Nuclear Waste Management XXVIII , 2004 , CC9.3
Copyright
Copyright © Materials Research Society 2004

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